1. Field of the Invention
The present invention relates to plate type dust collecting electrostatic precipitators and in particular to a spacer for maintaining proper spacing between the electrode collector plates within the electrostatic precipitator. More particularly, the invention relates to an electrode collector plate spacer which can be installed from the sides or from the top of the electrode collector plates and mounted in the desired position within the precipitator without dismantling the plates and their supporting structure and without permanently attaching the spacer to the plates.
2. Description of the Prior Art
In the generation of electrical energy by burning coal, oil and other fuels to produce steam for power generation, a certain amount of waste material in the form of dust, dirt particles, fly ash and other particulates are produced during combustion. In the past, these waste products have simply been discharged into the atmosphere. However in recent years, more stringent environmental protection laws and regulations governing the discharge of pollutants into the atmosphere have been enacted, requiring that a larger percentage of these waste particles be collected before discharge into the atmosphere. One type of apparatus for collecting particulates from combustion product gases is the electrostatic precipitator.
Electrostatic precipitators typically have a plurality of collector electrode plates which are spaced apart from, and oriented parallel to, one another. A plurality of corona electrode wires are disposed between the spaced plates. The collector plates consist of a series of joined metal panels. The plates are suspended from a support structure and are located a fixed horizontal distance from one another. The plurality of corona electrode wires located between the spaced plates are oriented vertically. The corona electrode wires impart a charge to the dust particles as they move through the spaces between the plates. The dust and other particles become charged at a different polarity than the electrode plates, whereby the charged particles are attracted to and collected on the electrode plates. Periodically the plates are cleaned, for example by shaking the plates, and the collected particulates are removed from the bottom of the precipitator.
One form of plate construction illustrated in FIG. 1 consists of a plurality of individual panels, the edges of which are bent into flanges which are interlocked with the flanges at the edges of adjacent panels. These interlocking flanges form outwardly projecting ribs 22 which extend vertically along the length of the collector plates. In addition to joining the individual panels into an electrode plate, the ribs 22 provide rigidity to the assembled plates enabling the plates to better maintain a flat parallel relationship with respect to the horizontally spaced adjacent plates.
It is desirable that as high a voltage as possible be applied across the electrode plates and corona electrode wires to collect particles passing between the plates more efficiently. It is therefore critical to maintain a constant horizontal spacing between neighboring plates, and in particular a constant spacing between the plates and the corona electrode wires extending therebetween, in order to prevent arcing between the wires and the plates and the subsequent destruction of the electrostatic field produced for collecting the dust particles. If a constant spacing cannot be maintained, the operating voltage must be reduced in order to prevent arcing with an attendant reduction in precipitation efficiency.
Precipitators having the particular collector electrode plate and corona electrode wire configuration described above, sometimes experience a serious problem of plate warping or bowing. Plate warping can occur during the life of the precipitator for a variety of reasons including cleaning (i.e., shaking) of the plates and the high temperature of the combustion gases passing over the plates. Plate warping seriously distorts the spacing between the electrode plates and the electrode wires and increases the danger of arcing, thereby necessitating a lower applied voltage and consequently resulting in a lower precipitation efficiency.
In order to eliminate or at least reduce plate warpage, various plate spacers and methods have been developed. A number of references disclose the use of spacer bars and/or cross braces which extend between adjacent plates in order to maintain interplate spacing. The great majority of these spacers are attached to one or more of the electrode plates, usually by welding. These braces extend horizontally between adjacent plates and provide sufficient strength and rigidity to maintain the plates in their spaced parallel relationship. Various types of these plate spacers are shown in U.S. Pat. Nos. 4,007,023; 4,239,514; 4,519,818; 4,478,614; and 4,479,813. Unfortunately, the installation of these kinds of spacers on existing electrostatic precipitators is extremely expensive and time consuming. A workman must enter between the spaced plates to mechanically attach the spacer to the plates, typically by welding, bolting or similar attachment procedure. This procedure can only be performed after the precipitator has been completely shut down and cooled since much of the supporting hardware for the plates and the corona wires must be removed in order to allow a workman sufficient space in which to work. This increases considerably the "down time" of the precipitator as well as the labor costs associated with the plate straightening procedure.
In response to these difficulties. Ahern in U.S. Pat. No. 4,559,064 developed a spacer comprising a rigid frame which slidably engages the vertically extending ribs on adjacent electrostatic precipitator plates. When a precipitator is new, the Ahern spacers can be installed without the necessity of a workman entering into the restricted space between adjacent plates. The frames are mounted over the ribs adjacent electrode plates, either at the top or the bottom of the precipitator, and slide along the ribs until reaching the desired vertical location within the precipitator. The frames clamp onto the ribs thereby enabling a workman standing outside the precipitator, using a long-handled tool, to slide the spacers into position between the plates purportedly without dismantling the precipitator.
Unfortunately, the Ahern spacers cannot be so easily installed on certain precipitators. For example on many precipitators of the above-described type, dimples are formed along the ribs in order to provide better interlocking between adjacent panels in a plate assembly. The Adhern spacers will not easily slide over these dimples. It is also not uncommon to encounter precipitator plates with ribs which have been crimped. Precipitator servicemen have in the past had modest success in straightening moderately bowed plates by crimping the ribs on the convex side of a bowed plate at spaced intervals along the rib. The Ahern spacer will not slide over the crimps introduced from such plate straightening attempts. In precipitators having severely warped plates, the plate warpage can cause the ribs to deform. The Ahern spacers will not easily slide over these deformed areas.
Accordingly, there has been a need in the art for an improved electrostatic precipitator plate which may be installed at any desired vertical position along the length of the collector electrode plates without requiring dismantling of the electrostatic precipitator and without requiring the spacer to be vertically positioned within the precipitator by sliding the spacer over a long vertical length of the collector plate ribs.
It is another object of the present invention to provide such an electrostatic precipitator plate spacer which is inexpensive and yet effective in maintaining the plates in a predetermined spaced relationship.
It is another object of the present invention to provide an improved plate spacer for electrostatic precipitators which can be installed from the side or from the top of the precipitator plates without requiring removal of the electrode supporting structure and which can be easily positioned at any desired position within the precipitator without requiring the installer to physically enter the space between the plates.
It is another object of the invention to provide such a plate spacer which does not need to be permanently attached to the plates but which instead can be positioned securely at any desired vertical position within the precipitator simply by compressively engaging the projecting ribs formed by the interlocking connection of adjacent collector panel edges.
It is yet another object of the present invention to provide an improved plate spacer which can be easily disengaged from the plates and repositioned at a different location along the plate ribs, either at the time of installation or after the spacer has been installed for a length of time in order to maintain parallel alignment of the horizontally spaced electrode plates throughout the vertical length thereof, and in which more than one spacer can be installed at desired locations along the length of the spaced plates in the event that plate warpage is serious enough to require a plurality of such spacers at various locations.
Another important object of the invention is to provide an improved plate spacer which can be rapidly installed in existing precipitators, thereby reducing the down time of the precipitator during spacer installation.